Pressure resistance is required for oil seal rings used in vehicle CVTs (continuously variable transmissions: stepless transmissions), power steering devices, etc. In order to satisfy the pressure resistance, for example, a modified polytetrafluoroethylene resin containing a polyfluoroalkyl group filled with glass fiber, etc., which originally has excellent pressure resistance, is used (see Patent Document 1). In this case, however, aggression against a mating metal used in a housing, etc., tends to be large.
Moreover, in order to facilitate the incorporation of a seal ring into an apparatus, one portion of the seal ring on its circumference is generally cut to provide an abutting portion. However, when the cut cross-sections of this portion are pressed by oil pressure and fixed to each other, the seal ring cannot be subsequently attached to the housing side. Therefore, it is difficult to seal oil when oil pressure is applied again, and the oil flows through the seal ring. The oil flowing through the seal ring causes defects, for example, the engine does not start.